FIG. 42 shows a ball bearing according to a first conventional example which is widely used to support various types of rotating portions. This ball bearing has a construction in which an inner ring 102 having an inner ring raceway 101 on an outer circumferential surface and an outer ring 104 having an outer ring raceway on an inner circumferential surface are arranged concentrically, and a plurality of balls 105 are arranged rollably between the inner ring raceway 101 and the outer ring raceway 103.
The plurality of balls 105 are retained rollably in a cage 107 shown in FIGS. 43, 44. The cage 107 is a crown type cage and is formed as a one-piece by injection molding of synthetic resin. The cage 107 includes an annular base portion 108 and a plurality of pockets 109 which are provided in an axial end face of the base portion 108. Each pocket 109 is formed by a recess portion 110 which is provided in the axial end face of the base portion 108 and a pair of elastic pieces 111 which are disposed at edges of the recess portion so as to face each other with a space provided therebetween. Facing surfaces of the pair of elastic pieces continue to an inner surface of the recess portion so as to form a spherical recess surface or cylindrical surface.
By pushing in the balls 105 individually between the pairs of elastic pieces 111 while press expanding the spaces defined therebetween by the balls 105, the cage 107 retains the balls 105 rollably in the corresponding pockets 109.
The cage 107 is formed of synthetic resin such as nylon 46, nylon 66, polyphenylene sulfide (PPS), polytetra fluorine ethylene (PTFE) and polyether ether ketone (PEEK), for example. In addition, it is known that toughness and mechanical strength can be increased under high-temperature environments by adding approximately 10 to 40 mass % reinforcement material such as glass fibers (GF) or carbon fibers (CF) to these synthetic resins.
In many cases, ball bearings like this are used under severe conditions such as high-temperature, high-speed conditions. For example, in the case of a ball bearing which is incorporated in a drive motor for a hybrid vehicle or a rotary supporting portion of an alternator, the ball bearing is used at high temperatures (100° C. or higher) and at high speeds (rotation speeds of 10000 min−1 or faster, or 0.6 million or larger in dmn value) in many cases. Note that dm of dmn denotes bearing pitch circle diameter (in mm), and n denotes bearing rotation speed (in min−1). In operating conditions like this, the cage 107 in the ball bearing rotates at high speeds together with lubricating oil or grease present between the outer circumferential surface of the inner ring 102 and the inner circumferential surface of the outer ring 104. Then, a complex force, which is in combination of a force directed radially outwards based on a centrifugal force, a restraining force based on the revolution of the balls 105 and stirring resistance of the lubricating oil or grease, is exerted on the cage 107 while it is rotating at high speeds.
The cage 107 repeats an irregular motion due to such a complex force and receives complex stress accompanied by an impact. Consequently, when the bearing continues to operate under the high-speed operating conditions, the cage 107 is elastically deformed or plastically deformed by the action of centrifugal force. These deformations tend to be promoted easily as the operating temperature increases. As a result, gaps between inner surfaces of the pockets 109 and rolling contact surfaces of the balls 105 come to vary largely. Further, the inner surfaces of the pockets 109 wear due to force exerted thereon from the rolling contact surfaces of the balls 105. Then, when the gaps become large, the following problems are caused.
Firstly, the cage 107 vibrates finely as the bearing rotates, whereby not only is the wear of the pockets 109 promoted, but also harmful vibration and noise are generated. Secondly, the restraint of the cage 107 by the balls 105 is released, as a result of which the cage 107 is displaced or made eccentric partly or entirely, and part of the cage 107 is caused to rub against the inner ring 102 or the outer ring 104.
For example, the elastic pieces 111 of the pocket 109 are deformed radially outwards based on the centrifugal force (see FIG. 45), and respective outer circumferential surfaces of each elastic piece 111 and the inner circumferential surface of the outer ring 104 rub against each other. When the outer circumferential surfaces and the inner circumferential surface rub against each other in such a way, there is caused a fear that the dragging torque of the bearing increased or the cage 107 breaks. In addition, when the wear progresses further, the cage 107 comes out of the bearing, and the bearing is disassembled, causing a fear that serious damage is made to the bearing unit.
In order to solve these problems, a resin cage including a metallic reinforcement member is proposed (see, e.g., JP 8-145061 A and JP 9-79265 A). Since the rigidity of the cage is increased, even when the bearing is used under high-temperature, high-speed conditions, the aforesaid deformations are less likely to be generated.
However, since the metallic reinforcement member is provided in the resin cage, the provision of the metallic reinforcement member constitutes a cause for an increase in the fabrication costs of such a ball bearing.
As shown in FIG. 46, a second conventional ball bearing has an inner ring 201 having an inner ring raceway surface 201a (a raceway groove) on an outer circumferential surface, an outer ring 202 having an outer ring raceway surface 202a (a raceway groove) on an inner circumferential surface, a plurality of balls 203 which are disposed rollably between the inner ring raceway surface 201a and the outer ring raceway surface 202a, and a resin crown type cage 204 which has an annular base portion 204a and pillar portions 204b provided on an axial end face of the base portion 204 so as to project therefrom and each having a claw portion at a distal end whereby the balls 203 are individually accommodated in spherical pockets 204c formed between the pillar portions 204b. The balls 203 are retained circumferentially at given intervals by the crown type cage 204 and revolve together with the cage 204.
When this type of ball bearing is used in a rotating portion such as a transmission of a motor vehicle, a forced feed lubrication system in which lubricating oil is supplied by a pump or the like is adopted in many cases. Lubricating oil flows through an interior of the bearing in an axial direction and circulates within the transmission unit for lubrication.
When this ball bearing is caused to rotate at high speeds, as shown in FIGS. 47A and 47B, the pillar portions 204b open radially outward about the base portion 204a of the crown type cage 204 as an axis of distortion. As a result, the contact surface pressure between a radially inner side of the spherical pocket 204c in the crown type cage 204 and the ball 203 is increased, whereby a radially inner portion 204p of the pocket 204c wears to be heated largely.
When the wear of the radially inner portion 204p of the pocket 204c progresses, the crown type cage 204 rotates with large run-out, and the crown type cage 204 vibrates. Further, as shown in FIG. 48, a radially outer side of the crown type cage 204 is brought into contact with the inner circumferential surface of the outer ring 202, and the pillar portion 204b wears, whereby in the worst case, there may be a situation in which the cage 204 fails.
On the other hand, as shown in FIGS. 49A and 49B, there is a proposal in which a center Oc of the spherical pocket 204c of the crown type cage 204 is disposed radially outer than a center T1 of a radial width of the crown type cage 204, that is, assuming that an overall radial width dimension of the crown type cage 204 is Q, an inner side width Q1 than the center Oc of the spherical pocket 204c is made larger than an outer side width Q2 so as to ensure that a ball holding amount on the radially inner side becomes larger, thereby making it possible to suppress the radially outward warp of the crown type cage 204 (see, e.g., JP 5-34317 A).
However, in the ball bearing shown in FIGS. 49A and 49B, when the bearing is rotated at high speeds, a sufficient amount of lubricating oil is not supplied to the radially inner side of the spherical pocket 204c due to centrifugal force, whereby the radially inner side wears, and finally, the warp cannot be suppressed, leading to a feat that the problem is caused by the rotation of the crown type cage 204 with run-out.
In addition, it is considered that a lubricating oil nozzle is disposed close directly to an inner ring 201 side of the crown type cage 204 to supply the lubricating oil into an inner circumferential portion thereof. However, as this occurs, the lubrication nozzle is necessary separately, and a space where to install the lubrication nozzle is also necessary.